The present invention generally relates to power conversion, and particularly relates to push-pull inverter circuits with snubber-based energy recovery.
Push-pull inverter circuits are commonly used in power conversion applications, such as in DC-to-AC power inverters. In terms of construction, such inverter circuits typically comprise a transformer with a switched primary winding having its center tap coupled to a source of DC power. Each end of the primary winding is coupled to a DC return through a switch, and output AC power is provided by the transformer's secondary winding based on alternately turning on one or the other switch at a desired frequency. Output voltage variations are achieved by varying the relative conduction intervals of the two switches, and the switching control signals can be generated as Pulse Width Modulation (PWM) signals of essentially any desired resolution.
As a general rule, push-pull inverter circuits must be provided with some form of a “snubber” circuit to limit switching-induced voltage transients on the primary winding. In a typical approach to snubbing, snubber diodes connect each end of the primary winding to a snubber capacitor. In this manner, the snubber diodes clamp the voltage at respective ends of the primary winding by dumping current into the snubber capacitor.
A resistive load can be used to discharge the snubber capacitor, however that approach simply dissipates the potentially significant energy captured by the snubber circuit as waste heat. In a more efficient approach, a buck converter circuit can be used to return energy from the snubber circuit to the inverter circuit's source voltage.
With this approach, a separate buck converter is added between the snubber circuit and the inverter's DC source supply. While the addition of separate buck converter for snubber energy recovery aids inverter efficiency by recovering some of the energy that otherwise would be lost to the snubber circuit, it also increases the cost and size of the inverter circuit.